Non-volatile magnetic random access memory (MRAM) devices have the potential to replace volatile dynamic random access memory (DRAM) devices and static random access memory (SRAM) devices in some applications. The MRAM devices include arrays of memory cells such as tunneling magneto-resistance (TMR), colossal magneto-resistance (CMR), and giant magneto-resistance (GMR) memory cells.
MRAM cells typically include “data” and “reference” layers. The data layer includes a writeable magnetic material, and the reference layer includes a fixed magnetic material. A dielectric layer in between the two has greater or lesser resistance to electrical current depending on whether the magnetic fields from the sandwiching layers are canceling or reinforcing one another.
During a write operation, the magnetization of the data layer can be switched between two opposite states by applying an electro-magnetic field through a nearby wire loop. Thus binary information can be stored. The reference layer usually includes a magnetic material in which the magnetization is pinned. A magnetic field applied to the data layer penetrates the reference layer with insufficient strength to switch the magnetization in the reference layer.
For example, in a TMR cell, the data layer and the reference layer are separated by a thin dielectric layer so that a tunneling junction is formed. The probability that electrons will be able to tunnel through the dielectric layer depends on the direction of the magnetization in the data layer relative to the direction of the magnetization in the reference layer. Therefore, the structure is “magneto-resistant” and information can be stored and retrieved by reading the magnitude of tunneling currents thereafter able to pass through the memory cell.
In general, the magnetic memory cells should be as small as possible. However, the smaller the cells are made, the more sensitive they are to thermal stability problems during operation. In order to compensate, the small magnetic memory cell data layers are fabricated with magnetic material that is more resistant to magnetic change. Unfortunately, generating the stronger fields necessary makes switching the memory cells more difficult during the write operation. Hence, there is a need for a magnetic memory device that addresses these concerns.